This invention relates to a method of preparing poly(arylene ether ketones) and to novel poly(arylene ether ketones).
Poly(arylene ether ketones), particularly those wherein a substantial fraction or all of the arylene groups are p-phenylene, possess many desirable properties, for example, high temperature stability, mechanical strength, and resistance towards common solvents. Among these, the poly(arylene ether ketone) having the repeat unit ##STR4## has been the focus of considerable attention. Bonner, in U.S. Pat. No. 3,065,205; Goodman et al., in GB No. 971,227; Jones, in GB No. 1,086,021; and Marks, in U.S. Pat. No. 3,441,538; each disclose the preparation of such a polymer by the Friedel-Crafts polymerization of tere- and/or isophthaloyl chloride with diphenyl ether. While such a synthetic approach is attractive because of the ready availability of the monomers, resulting polymer appears to have defects which limit its thermal stability and/or its melt processability and utility. Berr, in U.S. Pat. No. 3,516,966 reported that the all-para polymer was not melt-processable and degraded under melt processing conditions.
Angelo, in U.S. Pat. No. 3,767,620, addressed the problem of poor melt stability of certain poly(arylene ether ketones), stating: "[P]olyketones prepared from diphenyl ether and terephthaloyl and isophthaloyl halides in the presence of Friedel Crafts catalysts invariably contain 9-phenylenexanthydrol end-groups, generally in the amount of about 0.6 to 1.0 % by weight. These 9-phenylenexanthydrol end-groups have been found to be a major factor in the poor melt stability of this type of polyketone. " Angelo proposed treating the polymer with a reducing agent, converting the 9-phenylenexanthydrol groups to 9-phenylenexanthene groups. He found that 9-phenylenexanthydrol groups could be detected by UV-VIS spectroscopy thermally stable reduced polymer having an absorbance at 4550 521 of less than 0.18 and as-made, thermally unstable polymer having an absorbance of at least 0.20 and generally greater than about 0.25. While reduction may improve melt stability, the 9-phenylenexanthene groups, possessing tertiary hydrogen atoms, are themselves susceptible to air oxidation at elevated temperatures. Additionally, the method of Angelo requires a separate post-polymerization treatment step, which may be impractical on a large scale.
Sterzel, in U.S. Pat. No. 4,645,819, discloses that heat-stable poly(arylene ether ketone) may be prepared by polymerization of terephthaloyl chloride or fluoride and diphenyl ether in a homogeneous phase, for example anhydrous hydrogen fluoride with boron trifluoride catalyst. However, the boron trifluoride-hydrogen fluoride system requires special techniques and equipment, making this process difficult to practice on a commercial scale.
We have unexpectedly discovered that high molecular weight, melt-processable poly(arylene ether ketones) can be prepared by replacing the diphenyl ether in the monomer system with other monomers having two hydrogens activated towards displacement in a Friedel-Crafts polymerization. In particular, our invention enables the preparation of poly(arylene ether ketones) having the repeat unit ##STR5## without using diphenyl ether as a monomer and without using hydrogen fluoride-boron trifluoride as the polymerization medium, thus avoiding the above-described problems.